Let’s assume that the database migration should take place when the plugin is activated. Assuming your plugin is named myplugin, put this code in the myplugin.php file:

register_activation_hook(__FILE__, 'myplugin_install');

This makes WordPress execute the myplugin_install() method when the user activates your plugin.

Next, add this method:

function myplugin_install() {
  myplugin_migrate();
}

And our migration method:

function myplugin_migrate() {
  global $wpdb;

  $migs = myplugin_migrations();

  $current_migration = get_option('myplugin_current_migration', 0);
  $needed_migration = count($migs);

  for ($i = $current_migration; $i < $needed_migration; $i++) {
    $mig = $migs[$i];
    $wpdb->query($mig);
  }

  if ($current_migration == 0) {
    add_option('myplugin_current_migration', $needed_migration);
  } else {
    update_option('myplugin_current_migration', $needed_migration);
  }
}

What this does is that it runs through database statements (queries) returned from the myplugin_migrations() method. Let’s implement the actual migrations – add this method:

function myplugin_migrations() {
  global $wpdb;

  $migs = array();

  // Create example table
  $migs[] = '
  CREATE TABLE '.$wpdb->prefix.'myplugin_examples (
    id int(11) NOT NULL AUTO_INCREMENT,
    name varchar(255) NOT NULL,
    PRIMARY KEY (id)
  )';

  // Add examples
  $migs[] = "INSERT INTO ".$wpdb->prefix."myplugin_examples SET name='First example'";
  $migs[] = "INSERT INTO ".$wpdb->prefix."myplugin_examples SET name='Second example'";

  // Return the migrations
  return $migs;
}

That would create an example table and insert some values.

Now imagine that two months later you need a description field in your examples table. What do you do? It’s as easy as adding one line of code to the migrations:

// Add description field to examples
$migs[] = "ALTER TABLE ".$wpdb->prefix."myplugin_examples ADD description VARCHAR( 255 ) NOT NULL";

Deactivate and activate the plugin, and you table now has an extra field. Easy as cake!

Share your thoughts, opinions, and suggestions below.

Follow me on Twitter

I bought my MacBook on May 1th after viewing a screencast where a guy sets up a blog in 15 minutes using Ruby on Rails. I immediately said to my stepdad: “I’m going to buy a Mac and learn Ruby on Rails!”

And so I did – the day after, I bought a Mac.

I’ve always been a dedicated user of Microsoft‘s products. First C64, then Amiga, then Mac, then PC. I liked the way everything was tested and came from one place, unlike open source. I’ve always been saying stuff like “I like to pay for my software because then I’m be sure about the quality.” – but in reality, everyone who uses Windows and other Microsoft products know that this isn’t always the case.

So I bought the Mac, and the first thing that surprised me, was how much of day-to-day work was done in the Terminal, or command line. When I installed Ruby on Rails, it was via command line; when I installed plugins, it was via command line. Evererything command line.

Over the next few days I began to get a hang of it. I bought a couple of domain names and signed up for a slice at Slicehost – because I had read some job description that said that you should’ve at least tried to use a whole day of setting a slice.

Coming from Windows, Linux is a whole other deal to setup. I used a lot of the Slicehost articles that guides you through the whole process from setup and security to getting your slice to run as a webserver.

In the beginning I was a little nervous about all the command lines, if they would really work and so one. But the more you try it, the more calm you get. It just works! And lucky me there was a lot of helpful articles about Unix and Linux commands out there (just search for the command on Google).

Since starting out on the Mac, I’ve learned a multitude of things:

• Setting up an Ubuntu slice at Slicehost.
• Setting up a web server.
• Setting up Ubuntu Netbook Remix on my netbook.
• Setting up Ubuntu server at home, also on my netbook – which now functions as my testing server.
• Programming a little PHP – see Tweet My Cam.
• Programming Ruby on Rails.
• Tweaking some Java code, compiling and signing a java applet in one day – see a demo here.
• Download and compile software (configure, make, make install).
• Submitted a patch to a Ruby on Rails plugin on Github.
• Setting up WordPress and WordPress Mu blogs and making my own theme – see my private blog and private work blog.
• Setting up a Subversion repository at XP-Dev.com.
• Using the Subversion repository
• Loving Textmate as my favorite editor – also over Visual Studio.
• Plus a bunch of other things.

In short I’ve learned so much about the open source world that just wasn’t that easy on the Microsoft platform.

I still use Microsoft Windows and other products, but now it’s through VMware Fusion on the Mac.

I’m happy about the Mac because OS X is very unobtrusive, fast operating system and what it does, it does very good. But at the same time, I also want a netbook that’s easier to carry, so I may end up running both systems for different purposes (unless I’m just installing Ubuntu on the netbook too ).

Hope you found this post interesting – I wrote it to tell about a beautiful (yak, I know) progress from Windows to Mac and Linux. Thumbs up if this has made you want to try it too. And please tell me in the comments.

Follow me on Twitter